Jiminy release 1.8.1

[duburcqa]

• [core] Error and warning reporting more consistent with Python. ([core] Fix error estimation too optimistic for adaptive steppers. #716)
• [core] Fix exception handling for visco-elastic coupling and internal flex forces. ([core] Fix error estimation too optimistic for adaptive steppers. #716)
• [core] Fix error estimation too optimistic for adaptive steppers. ([core] Fix error estimation too optimistic for adaptive steppers. #716)
• [core] Fix partially broken step adjustment optim that could lead to integration fail. ([core] Fix partially broken step adjustment optim that could lead to integration fail. #721)
• [gym/common] Move 'sample' from 'spaces.py' to 'helpers.py'. ([core] Fix partially broken step adjustment optim that could lead to integration fail. #721)
• [gym/zoo] Fix 'acrobot' and 'cartpole' envs not using wrong integrator. ([gym/zoo] Fix 'acrobot' and 'cartpole' envs not using wrong integrator. #719)
• [misc] Do not verify metadata before pushing wheels on PyPi.
• [misc] Fix easy install doc. ([core] Fix partially broken step adjustment optim that could lead to integration fail. #721)
• [misc] Fix support of virtual env ('venv', 'pyenv', ...) when building dependencies. ([core] Fix partially broken step adjustment optim that could lead to integration fail. #721)